U.S. patent number 5,731,244 [Application Number 08/654,192] was granted by the patent office on 1998-03-24 for laser wire bonding for wire embedded dielectrics to integrated circuits.
This patent grant is currently assigned to Micron Technology, Inc.. Invention is credited to Sven Evers.
United States Patent |
5,731,244 |
Evers |
March 24, 1998 |
Laser wire bonding for wire embedded dielectrics to integrated
circuits
Abstract
A method and apparatus for connecting a lead of a lead frame to
a contact pad of a semiconductor chip using a laser or other energy
beam is herein disclosed. The lead may be wire bonded to the
contact pad by heating the ends of a wire until the wire fuses to
the contact pad and lead or an energy-fusible,
electrically-conductive material may be used to bond the ends of
the wire to the contact pad and lead. In addition, this invention
has utility for both conventional lead frame/semiconductor chip
configurations and lead-over-chip configurations. In addition, with
a lead-over-chip configuration, the lead may be directly bonded to
the contact pad with a conductive material disposed between the
lead and the contact pad.
Inventors: |
Evers; Sven (Boise, ID) |
Assignee: |
Micron Technology, Inc. (Boise,
ID)
|
Family
ID: |
24623832 |
Appl.
No.: |
08/654,192 |
Filed: |
May 28, 1996 |
Current U.S.
Class: |
438/617;
257/E21.517; 257/E23.034; 257/E23.039; 439/111 |
Current CPC
Class: |
H01L
21/4825 (20130101); H01L 23/49524 (20130101); H01L
24/80 (20130101); H01L 23/4951 (20130101); H01L
2924/01013 (20130101); H01L 2924/01029 (20130101); H01L
2924/0106 (20130101); H01L 2924/01082 (20130101); H01L
2924/14 (20130101); H01L 2924/01005 (20130101); H01L
2924/01006 (20130101); H01L 2924/01033 (20130101); H01L
2924/014 (20130101); H01L 2924/12042 (20130101); H01L
2924/12042 (20130101); H01L 2924/00 (20130101) |
Current International
Class: |
H01L
21/60 (20060101); H01L 23/48 (20060101); H01L
21/48 (20060101); H01L 21/02 (20060101); H01L
23/495 (20060101); H01L 021/60 () |
Field of
Search: |
;438/617,612,613,111,112 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Picardat; Kevin
Attorney, Agent or Firm: Trask, Britt & Rossa
Claims
What is claimed is:
1. A method for wire bonding a semiconductor chip to a lead frame,
said method comprising the steps of:
providing a bonding location for said wire bonding;
positioning at least one semiconductor chip having a plurality of
contact pads on a surface thereof at the bonding location, the
plurality of contact pads defining a first plurality of bonding
sites at the bonding location;
positioning a lead frame having a plurality of leads at the bonding
location, the plurality of leads defining a second plurality of
bonding sites at the bonding location;
providing a plurality of wires;
aligning a first portion of said plurality of wires relative to a
portion of the first plurality of bonding sites and a second
portion of said plurality of wires relative to a portion of the
second plurality of bonding sites; and
substantially simultaneously bonding the first portion and the
second portion of the plurality of wires with a directed energy
beam to a portion of the first bonding sites and to a portion of
the second bonding sites.
2. The method of claim 1, further including providing an
energy-fusible, electrically-conductive bonding material proximate
at least one of said plurality of first and second bonding
sites.
3. The method of claim 1, further including providing a foil that
at least partially supports said plurality of wires.
4. The method of claim 3, wherein said foil includes said
energy-fusible, electrically-conductive material proximate said
first portion and said second portion of said plurality of
wires.
5. The method of claim 4, wherein said foil is comprised of a
dielectric material, a plurality of wires embedded substantially
within said foil, said plurality of wires each having a first end
and a second end, and first and second energy-fusible,
electrically-conductive bonding material positioned proximate said
first and second ends, respectively.
6. The method of claim 2, including providing said semiconductor
die wherein said energy-fusible, electrically-conductive bonding
material is attached to said first and second plurality of bonding
sites.
7. The method of claim 1, including providing said at least one
semiconductor chip with at least one contact pad of said plurality
of contact pads located proximate a periphery of said at least one
semiconductor chip.
8. The method of claim 1, including providing said at least one
semiconductor chip with at least one contact pad of said plurality
of contact pads located proximate a center line of said at least
one semiconductor chip.
9. The method of claim 1, including providing said lead frame
having a lead-over-chip configuration.
10. The method of claim 1, wherein said energy beam includes a
laser beam.
11. The method of claim 1, wherein said energy beam includes a
focused light source.
12. The method of claim 1, wherein said energy beam includes a heat
source.
13. The method of claim 1, further including providing at least one
lens to focus said energy beam on to at least one wire of said
plurality of wires.
14. The method of claim 13, further including positioning an
optical flat between said energy beam and said at least one wire of
said plurality of wires, said optical flat comprising a plurality
of lenses, each of said plurality of lenses located within said
optical flat to focus said energy beam proximate said first and
second bonding sites.
15. The method of claim 1, further including providing at least one
reflective surface for directing said energy beam toward said first
and second pluralities of bonding sites.
16. The method of claim 1, further including providing at least one
deflective surface for directing said energy beam toward said first
and second pluralities of bonding sites.
17. The method of claim 14, further including providing at least
one prism to direct said energy beam toward said plurality of
lenses.
18. The method of claim 14, further including providing at least
one mirror to direct said energy beam toward said plurality of
lenses.
19. The method of claim 13, further including providing at least
one fiber optic segment to direct said energy beam toward said at
least one lens.
20. The method of claim 1, further including providing at least one
beam splitter for splitting said energy beam into more than one
energy beam.
21. The method of claim 1, further including providing an indexing
system to automatically index said at least one semiconductor die
and said at least one lead frame to said bonding location.
22. The method of claim 1 further including translating said energy
beam relative to said at least one semiconductor die.
23. The method of claim 15, further including directing said energy
beam by articulating said at least one reflective surface.
24. The method of claim 1, further including controlling said
energy beam with at least one microprocessor.
25. A method for wire bonding a semiconductor chip, comprising:
positioning at least one semiconductor chip having a plurality of
contact pads on a surface thereof and at least one lead frame
having a plurality of leads at a bonding location, said plurality
of contact pads and said plurality of leads defining a plurality of
bonding sites;
providing a plurality of wires;
aligning a first portion of one of said plurality of wires relative
to a first bonding site of said plurality of bonding sites and a
second portion of one of said plurality of wires relative to a
second bonding site of said plurality of bonding sites; and
substantially simultaneously fusing said first portion and said
second portion of one of said plurality of wires with a directed
energy beam to bond said first portion to said first bonding site
and said second portion to said second bonding site.
26. The method of claim 25, further including providing an
energy-fusible, electrically-conductive bonding material proximate
at least one of said first and second bonding sites.
27. The method of claim 25, further including providing a foil that
at least partially supports said plurality of wires.
28. The method of claim 27, wherein said foil includes said
energy-fusible, electrically-conductive material proximate said
first portion and said second portion.
29. The method of claim 28, wherein said foil is comprised of a
dielectric material, a plurality of wires embedded substantially
within said foil, said plurality of wires each having a first end
and a second end, and first and second energy-fusible,
electrically-conductive bonding material positioned proximate said
first and second ends, respectively.
30. The method of claim 26, including providing said at least one
semiconductor chip wherein said energy-fusible,
electrically-conductive bonding material is attached to said first
and second bonding sites.
31. The method of claim 25, including providing said at least one
semiconductor chip with at least one contact pad of said plurality
of contact pads located proximate a periphery of said at least one
semiconductor chip.
32. The method of claim 25, including providing said at least one
semiconductor chip with at least one contact pad of said plurality
of contact pads located proximate a center line of said at least
one semiconductor chip.
33. The method of claim 25, including providing said at least one
lead frame having a lead-over-chip configuration.
34. The method of claim 25, wherein said energy beam includes a
laser beam.
35. The method of claim 25, wherein said energy beam includes a
focused light source.
36. The method of claim 25, wherein said energy beam includes a
heat source.
37. The method of claim 25, further including providing at least
one lens to focus said energy beam onto at least one wire of said
plurality of wires.
38. The method of claim 37, further including positioning an
optical flat between said energy beam and said at least one wire of
said plurality of wires, said optical flat comprising a plurality
of lenses, each of said plurality of lenses located within said
optical flat to focus said energy beam proximate said first and
second bonding sites.
39. The method of claim 25, further including providing at least
one reflective surface for directing said energy beam toward said
first and second bonding sites.
40. The method of claim 25, further including providing at least
one deflective surface for directing said at least one energy beam
toward said first and second bonding sites.
41. The method of claim 40, further including providing at least
one prism to direct said energy beam toward said plurality of
lenses.
42. The method of claim 40, further including providing at least
one mirror to direct said energy beam toward said plurality of
lenses.
43. The method of claim 38, further including providing at least
one fiber optic segment to direct said energy beam toward at least
one lens of said of plurality of lenses.
44. The method of claim 25, further including providing at least
one beam splitter for splitting said energy beam into more than one
energy beam.
45. The method of claim 25, further including providing an indexing
system to automatically index said at least one semiconductor die
and said at least one lead frame to a bonding location.
46. The method of claim 25, further including translating said
energy beam relative to said at least one semiconductor die.
47. The method of claim 39, further including directing said energy
beam by articulating said at least one reflective surface.
48. The method of claim 25, further including controlling said
energy beam with at least one microprocessor.
49. A method for wire bonding a semiconductor chip, comprising:
positioning at least one semiconductor chip at a bonding location,
said at least one semiconductor chip having a plurality of contact
pads on a surface thereof;
positioning at least one lead frame having a plurality of leads
relative to said at least one semiconductor chip so that a
plurality of said plurality of leads is proximate to and extends at
least partially over a corresponding plurality of said plurality of
contact pads, said plurality of said plurality of leads and said
corresponding plurality of said plurality of contact pads defining
a plurality of bonding sites;
providing an energy fusible, electrically conductive material
between said plurality of said plurality of leads and said
corresponding plurality of said plurality of contact pads; and
substantially simultaneously fusing said energy-fusible,
electrically-conductive material associated with more than one of
said plurality of bonding sites with an energy beam to form an
electrical connection between said plurality of said plurality of
leads and said corresponding plurality of said plurality of contact
pads.
50. The method of claim 49, wherein each of said plurality of leads
defines an opening therein for passage of said energy beam to said
energy-fusible, electrically-conductive material.
51. The method of claim 49, further including building up said
plurality of said plurality of contact pads with said
energy-fusible, electrically-conductive material so that a top
surface of said energy-fusible, electrically-conductive material is
at least even with a surface of a passivation layer of said at
least one semiconductor chip.
52. The method of claim 49, further including forming at least one
protuberance on each of said plurality of said plurality of leads
at least equal to the depth of said plurality of contact pads of
said at least one semiconductor chip relative to a passivation
layer of said at least one semiconductor chip.
53. The method of claim 49, wherein said energy-fusible,
electrically-conductive material is an integral part of said
plurality of said plurality of leads.
54. A method for wire bonding a semiconductor chip to a lead frame,
said method comprising the steps of:
providing a bonding location for said wire bonding;
positioning a semiconductor chip having a plurality of contact pads
on a surface thereof at the bonding location, the plurality of
contact pads defining a first plurality of bonding sites at the
bonding location;
positioning a lead frame having a plurality of leads at the bonding
location, the plurality of leads defining a second plurality of
bonding sites at the bonding location;
providing a plurality of wires, a first portion of said plurality
of wires being located relative to a portion of the first plurality
of bonding sites and a second portion of said plurality of wires
being located relative to a portion of the second plurality of
bonding sites; and
substantially bonding at least two of the first portion and the
second portion of the plurality of wires with a directed energy
beam to a portion of the first bonding sites and to a portion of
the second bonding sites.
55. The method of claim 54, further including providing an
energy-fusible, electrically-conductive bonding material proximate
at least one of said plurality of first and second bonding
sites.
56. The method of claim 55, further including providing a foil that
at least partially supports said plurality of said wires.
57. The method of claim 56, wherein said foil includes said
energy-fusible, electrically-conductive material proximate said
first portion and said second portion.
58. The method of claim 57, wherein said foil is comprised of a
dielectric material, a plurality of wires embedded substantially
within said foil, said plurality of wires each having a first end
and a second end, and first and second energy-fusible,
electrically-conductive bonding materials positioned proximate said
first and second ends, respectively.
59. The method of claim 55, including providing said semiconductor
die wherein said energy-fusible, electrically-conductive bonding
material is attached to said plurality of first and second bonding
sites.
60. The method of claim 54, including providing said at least one
semiconductor chip with said at least one contact pad located
proximate a periphery of said at least one semiconductor chip.
61. The method of claim 54, including providing said semiconductor
chip with at least one of said plurality of contact pads located
proximate a center line of said semiconductor chip.
62. The method of claim 54, including providing said lead frame
having a lead-over-chip configuration.
63. The method of claim 54, wherein said energy beam includes a
laser beam.
64. The method of claim 54, wherein said energy beam includes a
focused light source.
65. The method of claim 54, wherein said energy beam includes a
heat source.
66. The method of claim 54, further including providing at least
one lens to focus said energy beam onto at least one of said
plurality of wires.
67. The method of claim 66, further including positioning an
optical flat between said energy beam and said at least one wire of
said plurality of wires, said optical flat comprising a plurality
of lenses, each of said plurality of lenses located within said
optical flat to focus said energy beam proximate said first and
second pluralities of bonding sites.
68. The method of claim 54, further including providing at least
one reflective surface for directing said energy beam toward said
first and second pluralities of bonding sites.
69. The method of claim 54, further including providing at least
one reflective surface for directing said energy beam toward said
first and second pluralities of bonding sites.
70. The method of claim 67, further including providing at least
one prism to direct said energy beam toward said plurality of
lenses.
71. The method of claim 67, further including providing at least
one mirror to direct said energy beam toward said plurality of
lenses.
72. The method of claim 67, further including providing at least
one fiber optic segment to direct said energy beam toward at least
one of said plurality of lenses.
73. The method of claim 54, further including providing at least
one beam splitter for splitting said energy beam into more than one
energy beam.
74. The method of claim 54, further including providing an indexing
system to automatically index said semiconductor die and said lead
frame to a bonding location.
75. The method of claim 54, further including translating said
energy beam relative to said semiconductor die.
76. The method of claim 69, further including directing said energy
beam by articulating said at least one reflective surface.
77. The method of claim 54, further including controlling said
energy beam with at least one microprocessor.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to wire bonding lead frames to
semiconductor dice and, more specifically, to wire bonding a lead
frame to a semiconductor die using a laser beam to provide the
energy necessary to bond or fuse a wire to a lead of a lead frame
and to a contact pad of a semiconductor die. The method and
apparatus of lead-to-chip bonding herein described is applicable to
either a conventional lead frame and chip arrangement or a
lead-over-chip (LOC) arrangement, in any instance, where the lead
of a lead frame is directly or indirectly bonded to the contact pad
of a semiconductor chip.
2. State of the Art
Various types of semiconductor chips are connected to lead frames
and subsequently encapsulated in plastic for use in a wide variety
of applications. A conventional lead frame is typically formed from
a single, continuous sheet of metal, typically by metal stamping
operations. The conventional lead frame includes an outer
supporting frame, a central semiconductor chip supporting pad and a
plurality of leads, each lead having, in turn, a terminal bonding
portion near the central chip supporting pad. Ultimately, the outer
supporting frame of the lead frame is removed after the wire bonds
between the contact pads of the semiconductor chip and the leads
are made and the semiconductor chip and lead frame have been
encapsulated.
In an LOC lead frame the lead frame, has no central chip supporting
pad with the semiconductor chip being held in position with respect
to the lead frame and leads by means of adhesive strips secured to
the leads of the lead frame and the semiconductor chip.
A typical apparatus and method for forming the wire bonds between
the contact pads on a semiconductor chip and the leads of lead
frames is illustrated in U.S. Pat. No. 4,600,138. As disclosed, a
bond head is shown moving from a first bonding location to a second
bonding location. The end of the wire is bonded to the first
bonding location by the bond head. The bond head moves vertically
away from the first bonding location to draw a length of wire
necessary to make the wire bond. The bond head is then moved to the
second bonding location with subsequent bonding of the wire to the
second bonding location. The bond head is then used to pull and
subsequently break away the remaining wire from the second bonding
location. The bond head is then ready to be moved to another first
bonding location for effecting another wire bond.
Typically, the bond head is heated to assist the formation of the
wire bond. The heat and subsequent pressure applied by the bond
head fuses the end of the wire to the contact pad. Ultrasonic
vibration in conjunction with a heated bond head may also be used
to affect a wire bond. Typically, there is a single bond head for
making all of the wire bonds of the semiconductor chip. As should
be recognized by those skilled in the art, such an operation is
inherently mechanical in nature and thus limited to the speed of
movement of the mechanical device.
One method of speeding up a conventional wire bonding process is to
provide the heat necessary to effect a wire bond by utilizing heat
generated from a laser beam to heat the bond head. Such apparatuses
are disclosed in U.S. Pat. No. 4,534,811 to Ainslie et al., and
U.S. Pat. No. 4,845,354 to Gupta et at. However, as the number of
connections per semiconductor chip increase and the size of the
leads decrease, such a bonding tool becomes impractical.
It has also been recognized in the art to use laser beams to form a
lead-to-chip bond. For example, a method for reflowing solder to
bond an electrical lead to a solder pad using a laser, in which the
solder pad, rather than the terminal, is irradiated by the laser
beam, is disclosed in U.S. Pat. No. 4,926,022 to Freedman. In
addition, in U.S. Pat. No. 5,274,210 to Freedman et al., electrical
connections may be made by coating conductive elements with a
non-flux, non-metallic coating material making it possible to use a
laser for bonding. The laser is either moved in a continuous sweep
around all of the connections or pulsed.
It has also been recognized in the art to use a laser beam to bond
the bumps of an integrated circuit to a tape automated bonding
(TAB) tape lead. TAB, in general, has been one attempt in the art
to increase the speed and efficiency of the chip-to-lead bonding
process. For example, in U.S. Pat. No. 4,978,835 to Luijtjes et al.
and U.S. Pat. Nos. 5,049,718 and 5,083,007 to Spletter et al., a
laser beam is directed onto the ends of the leads of a TAB
tape.
None of the previously mentioned prior art references, however,
have successfully utilized laser light to reduce the mechanical
limitations of the bonding process. More specifically, prior art
devices either move the device relative to the laser for every
bond, or a single laser beam to every bonding site. Thus, it would
be advantageous to provide an apparatus and method for forming wire
bonds using a laser in which the laser need not move for each bond
and where more than one bond can be made substantially
simultaneously.
SUMMARY
Accordingly, the present invention provides a bonding apparatus and
method of using the same for bonding any lead frame, either a
conventional lead frame or a lead-over-chip (LOC) lead frame, to a
semiconductor chip. Preferably, the semiconductor chip will include
at least one contact pad on its active surface for providing an
output, or input as the case may be, of the chip. Likewise, the
lead frame will include at least one lead to be connected to the
contact pad of the chip. The chip/lead frame arrangement may be one
where wire bonding is necessary to make the electrical connection
between the contact pad and the lead, or an LOC arrangement where
the lead of the lead frame extends over the active surface of the
chip and is bonded to the contact pad with a short wire or a bump
of solder. In either case, the bond required to make the connection
uses an energy beam from a beam-emitting energy source to provide
the energy necessary to make the connection.
In a chip/lead frame arrangement where a wire bond is used to make
the electrical connection, the wire is aligned with the contact pad
and the lead is subsequently bonded or fused to each using a
directed energy beam. A beam of energy is focused on the site of
the bond with a lens or plurality of lenses. Moreover, the wire may
be directly bonded or fused to the contact pad and lead by melting
the wire with the energy beam, or an energy fusible, electrically
conductive bonding material may be provided proximate the bonding
site.
In a preferred embodiment, the wire bonds at the contact pad and at
the lead are substantially simultaneously bonded or fused. This may
be accomplished by using more than one beam emitting energy source
to direct more than one beam of energy, each to a different bonding
site, or providing a single beam emitting energy source and
splitting the beam into more than one smaller beam and directing
the smaller beams to different bonding sites.
The beam emitting energy source used in conjunction with the
present invention may be of various types known in the art. For
example, the energy source may emit a laser beam, such as that
produced by a pulsed solid state laser, a carbon dioxide laser, a
Nd:YAG laser, or a Nd:YLF laser, a focused beam of light, a beam of
radiant energy such as an electron beam, or a heat source, etc. In
any case, the energy beam is preferably directed to the bonding
site by prisms, mirrors, fiber optics, lenses and/or other
reflective and/or deflective surfaces or combinations thereof. More
specifically, in one preferred embodiment, each beam of energy is
directed by prisms or mirrors from the energy source toward each
bonding site. At least one lens is provided between each bonding
site and the prisms or mirrors to further focus the beam of energy
onto the bonding site. Each lens may be individually supported by a
frame-like support structure or contained within an optical flat in
which a plurality of lenses is formed. For a frame-like structure,
the lenses may be moved and/or oriented to accommodate different
chip/lead frame configurations. If the lenses are contained in an
optical flat, a different optical flat may be used to accommodate
various chip/lead frame configurations. In addition, the reflective
and/or deflective surface may be articulatable to direct the energy
beam to various bonding sites. With such an articulatable
configuration, various configurations of lead frames and chips can
be accommodated with the present invention.
In use, the energy beams are directed to a first set of bonding
sites until the heat generated from the energy beams creates the
bonds or fuses the bonds (i.e., wire bond or LOC bond) associated
with the first set. The apparatus then translates the energy beams
relative to the chip to a second set of bonding sites to make a
second set of bonds. This process is repeated until all of the
bonds associated with the chip/lead frame arrangement are
formed.
An indexing system may also be associated with the apparatus to
index chips, lead frames and other components into and out of the
bonding location. The indexing system may comprise conveyors,
articulating arms, magazines for housing the semiconductor device
components, and other equipment known in the art. In addition, the
entire system, from controlling the operation of the energy source
to controlling which set of bonding sites are bonded to indexing
the semiconductor device components, is controlled by at least one
or more microprocessors.
As previously mentioned, a semiconductor chip bonded to its
associated lead frame in accordance with the present invention may
have a conventional configuration where the contact pads are
positioned proximate the periphery of the chip or a LOC
configuration where the contact pads are positioned closer to a
center line of the chip. In either case, in a preferred embodiment,
a thin, flexible dielectric material (foil) containing fully or
partially embedded wires may be placed at least partially over the
surface of the chip containing the contact pads and the leads of
the lead frame. When properly positioned, the wires extend from the
contact pads to the leads of the lead frame. The foil may be
adhesively attached to the chip and/or lead frame, held in place by
a slight vacuum, or retained by a suitable clamping device in order
to maintain proper alignment of the wires relative to the chip and
lead frame. At the ends of each wire, an energy bondable, fusible,
electrically conductive material (such as solder) may be provided
for bonding the ends of the wire to the semiconductor chip and lead
frame. Similarly, the energy bondable, fusible, electrically
conductive material may be attached to the contact pads of the chip
and/or the leads of the lead frame prior to positioning of the foil
such that the energy fusible, electrically conductive material may
be heated and subsequently bonded to the ends of each wire.
For an LOC configuration where the leads of the lead frame extend
over the contact pads, an energy bondable, fusible, electrically
conductive material (e.g., solder) may be provided between the lead
and the contact pad. The solder may be bumped onto the contact pads
by methods known in the art or attached to the ends of the leads to
define a protuberance on the end of the lead so that when the lead
frame is superimposed over the chip, the protuberance of solder is
positioned above each contact pad. The solder may be bonded or
fused to make the electrical connection between the leads and the
contact pads by heating the leads themselves with an energy beam or
providing leads that define openings through which the beam may be
directed directly onto the solder. In yet another preferred
embodiment, the ends of the leads themselves may be configured to
contact the contact pads and may be bonded directly thereto by
heating the lead.
A preferred embodiment of a semiconductor device manufactured
according to the present invention would comprise a semiconductor
chip having a plurality of contact pads, a lead frame having a
plurality of leads, a foil layer or other suitable type material
having a plurality of wires at least partially embedded therein,
and a laser-bondable, electrically-conductive material making the
electrical connections between the wires and the contact pads and
leads.
Although the bonding apparatus of the present invention has been
described in relation to several preferred embodiments, it is
believed that a major advantage of the apparatus according to the
present invention is the efficient use of a beam emitting energy
source, such as a laser, to quickly and efficiently bond a lead
frame to a semiconductor chip by reducing the mechanical movements
generally associated with prior art bonding apparatuses. This and
other features of the invention will become apparent from the
following detailed description taken in conjunction with the
accompanying drawings and as defined by the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic side view of a first embodiment of the
laser-bonding apparatus according to the present invention;
FIG. 2 is a schematic top view of an optical flat used in the
laser-bonding apparatus in FIG. 1;
FIG. 3A is a schematic bottom view of a wire-embedded foil
according to the present invention;
FIG. 3B is a schematic side view of a wire-embedded foil shown in
FIG. 3A;
FIG. 4 is a schematic side view of an LOC configuration according
to the present invention;
FIG. 5 is a schematic side view of a second embodiment of the
laser-bonding apparatus according to the present invention;
FIG. 6 is a partial top view of a second embodiment of a lead of an
LOC lead frame shown in FIG. 5;
FIG. 7 is a schematic side view of a third embodiment of the
laser-bonding apparatus according to the present invention;
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT
As illustrated in FIG. 1, the laser-bonding apparatus 10 is
comprised of a plurality of lasers 12, 14, 16, and 18 emitting
laser beams 20, 22, 24, and 26, respectively. The laser beams 20,
22, 24, and 26 are directed toward lenses 28, 30, 32, and 34,
respectively, by prisms 36, 38, 40 and 42. The lenses 28, 30, 32,
and 34 focus the laser beams 20, 22, 24, and 26 onto the bonding
sites 44, 46, 48, and 50, respectively, associated with the
semiconductor chip 52 and lead fingers or leads 54 and 68 of a lead
frame. The lenses 28, 30, 32, and 34 are formed in a frame-like
structure or an optical flat 56 above each bonding site 44, 46, 48
and 50.
The optical flat 56 as shown in FIG. 2 has a plurality of lenses
57, 59, 61, and 63, such as lenses 28, 30, 32 and 34, formed in
longitudinal rows along the length of the optical flat 56
corresponding to the bonding sites of a chip 52 and lead fingers 54
and 68, such as bonding sites 44, 46, 48, and 50. As illustrated by
the arrow and bar 65, the laser beams 20, 22, 24 and 26 are
incrementally moved across the optical flat from one set of lenses
57, 79, 61, and 63 to the next until all of the bonds have been
fused located on with a particular chip 52 and lead fingers 54 and
68.
The semiconductor chip 52 and lead fingers 54 and 68 are supported
on a platform or chip support 58. The chip support 58 may be heated
so that heat generated by the laser beams 20, 22, 24, and 26 at the
bonding sites 44, 46, 48, and 50 do not create such an extreme
point of localized heating that could stress the chip 52 and/or the
lead fingers 54 and 68. In addition, the chip support 58 may
include structure as is known in the art to help align the lead
fingers 54 and 68 relative to the chip 52 and the chip 52 relative
to the rest of the laser-bonding apparatus 10.
In order to secure and align the wires 60 necessary to make wire
bonds between the chip 52 and the lead fingers 54 and 68, as
illustrated in FIGS. 3A and 3B, a foil, relatively-thin dielectric
material, or other suitable material 62 may be used to support a
plurality of wires 60. The wires 60 may be fully or partially
embedded in the foil 62 so long as the foil 62 can maintain the
relative positions of the wires 60. At the end of each wire 60, an
energy-bondable, fusible, electrically-conductive material 64, such
as solder or other material known in the art, may also be provided
to make the bond between the wires 60 and the bond sites 44, 46,
48, and 50. A flux may also be applied to the ends 66 of the wires
60 to help the wires 60 bond to the bonding sites 44, 46, 48, and
50, whether an energy-bondable, fusible, electrically conductive
material 64 is used or not.
As shown in FIGS. 1 and 3B, the foil 62 is contoured to fit over
the chip 52 and extend down to the lead fingers 68 of the lead
frame 54. This contoured shape may be formed into the foil by
bending the foil to correspond to the shape of the chip 52/lead
fingers 54 and 68 configuration or may take this shape due to the
foil's 62 flexible nature. Because the foil 62 is relatively thin
and flexible, it may be necessary to retain the foil 62 relative to
the chip 52 and lead fingers 54 and 68 during the bonding process.
Retaining the foil 62 may be accomplished by applying an adhesive
to the underside 70 so that the foil 62 may be adhesively bonded to
the chip 52 and/or the lead fingers 54 and 68. In addition to or in
lieu of adhesive retaining, the foil 62 may be secured during
bonding by retaining members 72 and 74 that hold the foil 62
relative to the lead fingers 54 and 68 and a resilient pad 76 that
holds the foil 62 in place relative to the chip 52. Moreover, the
foil 62 may be retained by providing a slight vacuum to the
underside 70 of the foil 62 to draw the foil 62 onto the leads 68
and the chip 52.
In addition, to a conventional chip 52/lead fingers 54 and 68
arrangement as illustrated in FIG. 1, the laser-bonding apparatus
10 of the present invention can also be used to wire bond a LOC
arrangement, as illustrated in FIG. 4, where the leads 80 of the
lead frame 82 extend over the active surface 84 of the chip 86.
Typically, such a chip 86 will have a plurality of contact pads 88
proximate the center of the chip 86. Thus, in order to shorten the
length of the wires 90 necessary to make an electrical connection
between the lead 80 and the contact pad 88, the leads 80 extend
over the active surface 84 proximate the contact pads 88. A foil 92
containing wires 90 may also be used to house and support the wires
90 in a similar manner to the foil 62 described in relation to
FIGS. 3A and 3B. In addition, retaining members 94, 96, and 98 may
also be incorporated into the bonding apparatus 10 to retain the
foil relative to the chip 86 and lead frame 82 during the bonding
process.
In an alternate embodiment of the laser-bonding apparatus 100
depicted in FIG. 5, a LOC arrangement 101 is being bonded using a
single laser 102. In this LOC arrangement 101, however, as opposed
to that illustrated in FIG. 4, the lead fingers or leads 104 and
105 of the lead frame 112 are being bonded directly to the contact
pads 106 and 107, respectively, of the chip 108. In order to
substantially simultaneously bond the leads 104 and 105 to the
contact pads 106 and 107, respectively, the laser beam 110 is split
by a beam splitter 114, as is known in the art. The two beams 116
and 118 are directed to focusing lenses 120 and 122 by mirrors or
prisms 124 and 126. The focusing lenses 120 and 122 focus the beams
116 and 118 onto the bonding sites 128 and 130. The lenses 120 and
122 may be moved to accommodate various chip/lead frame
configuration and/or articulatable to direct the beams 116 and 118
to various bonding sites. The prisms 124 and 126 may also be
movable and/or articulatable in the x-axis, y-axis, and z-axis.
Because the passivation layer 132 of the chip 108 typically extends
above the contact pads 106 and 107, in order to make contact with
the leads 104 and 105, either a protuberance or other extension
must be provided on the leads 104 and 105 or the contact pads 106
and 107 must be raised at least to the level of the passivation
layer 132. If a filler material 134 is used, the filler material
134 should be conductive to provide an electrical path between the
contact pads 106 and 107 and the leads 104 and 105. Moreover, the
filler material 134 must be bondable or fusible by the energy
provided by the beams 116 and 118. In addition, the leads 104 and
105 should be held in position relative to the passivation layer
132 by a retainer, such as clamps 142 and 144. The chip 108 may
also be held in position by a recess 146 defined by the chip
support 148 sized and shaped to securely hold the chip 108 in place
during bonding.
When bonding or fusing the leads 104 and 105 to the contact pads
106 and 107, respectively, the top surfaces 136 and 138 of the
leads 104 and 105, respectively, may be heated by the beams 116 and
118, or, as illustrated in FIG. 6, an aperture or opening 140 can
be provided in each of the leads, such as lead 104, to expose the
filler material 134 directly to the beam 116.
Referring now to FIG. 7, a plurality of fiber optics 150, 152, 154,
and 156 are used to direct the laser beams 158, 160, 162, and 164
emanating from the lasers 166, 168, 170 and 172, respectively. That
is, as will be recognized by those skilled in the art, there may be
other ways known in the art to direct the laser beams 158, 160, 162
and 164 from the lasers 166, 168, 170 and 172 to the lenses 174,
176, 178 and 180.
In all of the preferred embodiments of bonding apparatus according
to the present invention, the manipulation of the lasers as well as
the indexing of chip components, such as the foil, die and lead
frames, can be automated and controlled by one or more
microprocessors 200 as is known in the art.
It should be noted that the laser source is preferably any
high-power, pulsed, solid state or continuous wave laser, such as
Nd:YAG, Nd:YLF, Ar-ion, CO.sub.2, Cu vapor, or other suitable
lasers known in the art, or a focused beam of light or a beam of
energy or radiant energy, such as an electron beam or heat source.
It should be recognized by those skilled in the art that the
apparatus according to the present invention may be used on any
semiconductor chip and associated lead frame having either
conventional configurations as is known in the art or a specialized
arrangement. Those skilled in the art will also appreciate that the
number of lasers and beams therefrom may be increased or decreased,
depending on the number of wire bonds to be formed at substantially
the same time. Further, the invention may be practiced on many
semiconductor devices where wire bonding or LOC bonding is desired
such as bonding a chip to a printed circuit board. Thus, the terms
"chip" and "lead frame" as used herein are intended as exemplary
and not limiting, the invention having applicability to any
semiconductor-related structure employing a wire bond or a LOC-type
bond. It will also be appreciated by one of ordinary skill in the
art that one or more features of any of the illustrated embodiments
may be combined with one or more features from another to form yet
another combination within the scope of the invention as described
and claimed herein. Thus, while certain representative embodiments
and details have been shown for purposes of illustrating the
invention, it will be apparent to those skilled in the art that
various changes in the invention disclosed herein may be made
without departing from the scope of the invention, which is defined
in the appended claims.
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